<style>
    .current{color:darkgreen}
    .state{font-size:16px;color:darkgreen}
    .logout{margin-left:20px; margin-bottom: 15px}
    .logout a{color:cornflowerblue;text-decoration: none}
    .logout a:hover{text-decoration: underline;}
</style>
<h1>会员管理注册系统</h1>
    <?php
        if(isset($_SESSION['loginUsername']) && $_SESSION['loginUsername'] != null)
        {
    ?>
    <dir class="state">当前登录：<?php echo $_SESSION['loginUsername']; ?>

        <span style="color:darkblue "><?php if($_SESSION['isAdmin']) echo "[管理员]"; ?></span>
        <span class="logout"><a href="logout.php">注销登录</a></span> </dir>
    <?php
        }
        $id =$_GET['id'] ?? 1;  //只使用同意php7
    ?>
<h2>
    <a href="index.php?id=1" <?php if($id==1) { ?> class="current" <?php } ?>>首页</a>
    <a href="signup.php?id=2" <?php if($id==2) { ?> class="current" <?php } ?>>会员注册</a>
    <a href="login.php?id=3" <?php if($id==3) { ?> class="current" <?php } ?>>会员登录</a>
    <a href="modify.php?id=4&source=member" <?php if($id==4) { ?> class="current" <?php } ?>>个人资料修改</a>
    <a href="admin.php?id=5" <?php if($id==5) { ?> class="current" <?php } ?>>后台管理</a>
</h2>